Having a `theme.json` file present results in Lumo utilities being loaded (v25)

[sissbruecker]

Description of the bug

If the legacy theme folder contains a theme.json then, regardless what the content of that file is, the Lumo utility classes are loaded. In my case I have an empty JSON object in that file: {}. If there is no theme.json then utilities are not loaded.

This is not the case in v24, where utility classes are only loaded if utility is listed in lumoImports.

Expected behavior

Either lumoImports should work correctly and only include utilities if utility is listed.

Or, if we want to drop support for lumoImports in v25, then utilities should never be loaded, unless they are explicitly added as an import through a CSS file, or through StyleSheet.

Minimal reproducible example

• Clone this repo: https://github.com/sissbruecker/vaadin-25-theme-test
• In lumo-theme-folder, add a theme.json with this content: {}
• Run the app in lumo-theme-folder
• Observe that Lumo utilities are loaded on the page

Versions

• Vaadin / Flow version: 25 alpha 12
• Java version: 21